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K.C.S.E Physics Q & A - MODEL 2012PP2QN018

21/7/2020

K.C.S.E Physics Q & A - MODEL 2012PP2QN018

 Figure 18 shows parts of an x-ray tube.

(a) Explain why:
(i) A potential difference is applied to the filament.
(ii) A high potential difference is applied between the cathode and the anode.
(iii) Most of the tube is surrounded by lead.
(b) State how the resulting x-rays are affected by increasing the potential difference between the anode and the cathode.
(c) Light of frequency 7.5 x 10¹⁴ Hz strikes a metal surface whose work function is 4.0 x 10^-19J. Determine the kinetic energy of the emitted photoelectrons. (take planks constant h = 6.63 x 10^-34 Js)

answers

(a) (i) To produce electrons; by thermionic emission;
(ii) To accelerate the electrons to give them enough K.E. t produce X-rays at the anode;
(iii) To absorb stray X-rays, thus protecting the operator from those rays;
(b) Increases K.E. of electrons and hence causes X-rays of higher frequency;
OR
X - ray are more penetrative
X - rays of shorter wavelength.

K.C.S.E Physics Q & A - MODEL 2012PP2QN018

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State why alternating current (a.c) is used for transmitting electricity over long distances

K.C.S.E Physics Q & A - MODEL 2012PP2QN11

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K.C.S.E Physics Q & A - MODEL 2012PP2QN02

Figure 2, shows two mirrors PQ and QR inclined at an angle of 1100. A ray of light is incident on mirror PQ at an angle of 600

Complete the diagram to determine the angle of reflection of the ray in the mirror QR

K.C.S.E Physics Q & A - MODEL 2012PP2QN01

K.C.S.E Physics Q & A - MODEL 2012PP1QN19

K.C.S.E Physics Q & A - MODEL 2012PP1QN18

Given that the density of water is 1000 kgm3 and that of wood is 800 kgm3, determine the; (i) Volume of the log. (ii) Upthrust on the log. (iii) Tension in the string.

K.C.S.E Physics Q & A - MODEL 2012PP1QN17

(d) An immersion heater rated 2.5 kW is immersed into a plastic jug containing 2 kg of water and switched on for 4 minutes. Determine; (i) the quantity of heat gained by the water; (ii) the temperature change for the water; (take specific heat capacity of water as 42 x 103Jkg-1K-1).

K.C.S.E Physics Q & A - MODEL 2012PP1QN16

K.C.S.E Physics Q & A - MODEL 2012PP1QN15

K.C.S.E Physics Q & A - MODEL 2012PP1QN14

K.C.S.E Physics Q & A - MODEL 2012PP1QN13

Figure 4 shows a graph of temperature against time when pure melting ice at 00 C is heated uniformly.

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Figure 2, shows two mirrors PQ and QR inclined at an angle of 110⁰. A ray of light is incident on mirror PQ at an angle of 60⁰

Given that the density of water is 1000 kgm³ and that of wood is 800 kgm³, determine the; (i) Volume of the log. (ii) Upthrust on the log. (iii) Tension in the string.

(d) An immersion heater rated 2.5 kW is immersed into a plastic jug containing 2 kg of water and switched on for 4 minutes. Determine;
(i) the quantity of heat gained by the water;
(ii) the temperature change for the water;
(take specific heat capacity of water as 42 x 10³Jkg^-1K^-1).

Figure 4 shows a graph of temperature against time when pure melting ice at 0⁰ C is heated uniformly.